Boiler with integrated economizer

ABSTRACT

A boiler comprises a boiler gas exhaust providing an exhaust for recuperated gases; and a secondary heat exchanger comprising: an economizer cold fluid inlet connected to a source of cold fluid; an economizer cold fluid outlet fluidly connected to the economizer cold fluid inlet and located thereabove, the cold fluid circulating upwardly from the economizer cold fluid inlet towards the economizer cold fluid outlet; a hot gas inlet for receiving the recuperated gases from the boiler gas exhaust; and a hot gas outlet fluidly connected to the hot gas inlet through the secondary heat exchanger, the recuperated gases circulating from the hot gas inlet toward the hot gas outlet; wherein the recuperated gases cross the secondary heat exchanger and exhaust by the hot gas outlet, the cold fluid being heated between the economizer cold fluid inlet and the economizer cold fluid outlet thereby resulting in a preheated fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of US provisional patent application 61/860,073 filed Jul. 30, 2013, the specification of which is hereby incorporated by reference.

BACKGROUND

(a) Field

The subject matter disclosed generally relates to the field of boilers for heating a fluid. More particularly, this description relates to boilers with tubes.

(b) Related Prior Art

Boilers with tubes, for heating a cold fluid (e.g., water, steam, thermal oil or any other heating medium) with hot gases are well known. Many improvements have been suggested over time. In order to enhance the efficiency, the number of gas passages was increased by adding separators, plates or baffles among the tubes. These additional parts among the tubes are exposed to the gases and thus require maintenance and decrease the availability of the boiler and they provide only a small increase in efficiency.

In order to further enhance the efficiency, external economizers are installed at the boiler gas outlet for recuperating the remaining energy in the gases exhausting the boiler. This type of economizer is separated from the boiler and needs external assistance (e.g., a pump) in order to achieve uninterruptable circulation of the cold fluid through the economizer.

For example, when a boiler is equipped with an external economizer, a continuous supply of cold fluid is needed to avoid vaporizing the cold fluid in the economizer (i.e., a modulation type of supply for example, including a level transmitter and a modulation valve). This equipment alone may be very expensive.

Also, the transfer of the hot and cold fluids from the economizer to the boiler is performed with a particular pattern of pipes and ducts between the economizer and the boiler. This increases the installation costs and therefore the return on investment.

There is therefore a need for a boiler with an integrated economizer to increase the global efficiency of boilers and to improve the return on investment.

SUMMARY

According to an embodiment, there is provided a boiler for heating a cold fluid with recuperated gases. The boiler comprises a boiler gas exhaust providing an exhaust for the recuperated gases; and a secondary heat exchanger comprising: an economizer cold fluid inlet connected to a source of cold fluid; an economizer cold fluid outlet fluidly connected to the economizer cold fluid inlet and located thereabove, the cold fluid circulating upwardly from the economizer cold fluid inlet towards the economizer cold fluid outlet; a hot gas inlet for receiving the recuperated gases from the boiler gas exhaust; and a hot gas outlet fluidly connected to the hot gas inlet through the secondary heat exchanger, the recuperated gases circulating from the hot gas inlet toward the hot gas outlet; wherein the recuperated gases cross the secondary heat exchanger and exhaust by the hot gas outlet, the cold fluid being heated between the economizer cold fluid inlet and the economizer cold fluid outlet thereby resulting in a preheated fluid.

According to an aspect, the secondary heat exchanger comprises a secondary shell for conveying the recuperated gases from the boiler gas exhaust.

According to an aspect, the secondary heat exchanger comprises a plurality of secondary tubes between the economizer cold fluid inlet and the economizer cold fluid outlet and within the secondary shell, the plurality of secondary tubes being fluidly connected to the source of cold fluid.

According to an aspect, main heat exchanger comprises a main shell receiving the preheated fluid.

According to an aspect, the main shell comprises a boiler cold fluid outlet near a bottom portion of the main shell and the source of cold fluid is connected to the boiler cold fluid outlet and whereby the cold fluid flows upwardly by natural circulation into and through the secondary heat exchanger.

According to an aspect, the boiler further comprises an external cold fluid inlet wherein the source of cold fluid is also connected to external cold fluid inlet to admit cold fluid from an external source.

According to an aspect, the boiler further comprises a flow restrictive device located near the boiler cold fluid outlet and an external cold fluid inlet, the flow restrictive device letting the cold fluid flow from the boiler cold fluid outlet to the economizer cold fluid inlet when there is no fluid flow from the external source and, when the level of cold fluid is too low in the boiler, the cold fluid flows from the external source and the flow restrictive device will close to let the cold fluid flow from the external source through the external cold fluid inlet and further prevent the cold fluid from the external source to flow directly in the main shell.

According to an aspect, the secondary shell is connected to or extends from the main shell.

According to an aspect, the main shell and secondary shell form a single shell.

According to an aspect, the main heat exchanger comprises two ends and the secondary heat exchanger is located at at least one of the two ends.

According to an aspect, the boiler further comprises a main heat exchanger for heating the preheated fluid, the main heat exchanger comprising the boiler gas exhaust and a burner for producing hot gases directed to the boiler gas exhaust.

According to an aspect, the boiler further comprises a lower header fluidly connected to the economizer cold fluid inlet.

According to an aspect, the boiler further comprises an upper header being fluidly connected to the economizer cold fluid outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1 is a perspective internal view of a boiler in accordance with an embodiment;

FIG. 2 is another perspective internal view of the boiler of FIG. 1;

FIG. 3 is a side view of the boiler of FIG. 1;

FIG. 4 is an end view of the boiler of FIG. 1 which shows the secondary heat exchanger;

FIG. 5 is a side view of the boiler of FIG. 1, showing the hot gases passages; and

FIG. 6 is a side view of the boiler of FIG. 1, showing the cold fluid passages.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

In embodiments there is disclosed a boiler with an integrated economizer; i.e., with a primary heat exchanger (aka, the boiler) and a secondary heat exchanger (aka, the economizer).

Referring now to the drawings, and more particularly to FIGS. 1-4, there is shown a boiler 10 for heating a cold fluid coming from a lower header 48 with recuperated gases 44 exiting a main heat exchanger 12 at its boiler gas exhaust 61. The boiler 10 includes a main heat exchanger 12 and a secondary heat exchanger 22. The main heat exchanger 12 further has two ends 14, 16.

The main heat exchanger 12 heats a preheated fluid 42; i.e., cold fluid is previously heated within the secondary tubes 26 of the secondary heat exchanger 22 which is rejected in the boiler 10 as a fluid/vapor mix that circulates outside of a plurality of primary tubes 20.

The main heat exchanger 12 includes a main shell 18 (FIG. 3) for receiving the preheated fluid 42 to be heated and a plurality of primary tubes 20. It is to be noted that the main shell 18 and the secondary shell 24 are not shown on FIGS. 1 and 2. Additionally, it is to be noted that the main shell 18 and secondary shell 24 may be integrated so as to form one and only one shell (i.e., the secondary shell 24 may be the extension of the main shell 18 at one end, at the other end, or at both ends of the boiler 10). The plurality of primary tubes 20 is within the main shell 18 and is for conveying the hot gases 40. The hot gases 40 are for heating the preheated fluid 42 which circulates within the main shell 18.

The source for the cold fluid via the lower header 48 is either from an external source 38 through external cold fluid inlet 30 or from a boiler cold fluid outlet 63 from the boiler 10 through a flow restrictive device (shown in FIG. 6) when level of water within the boiler 10 is sufficiently high. According to an embodiment, the flow restrictive device is a check valve.

The check valve is located near the boiler cold fluid outlet 63. The flow restrictive device lets the cold fluid flow from the boiler cold fluid outlet 63 to the economizer cold fluid inlet 49 when there is no fluid flow from the external source 38. When the level of cold fluid is too low in the boiler 10, the cold fluid flows from the external source 38 and the flow restrictive device will close to let the cold fluid flow from the external source 38 through the external cold fluid inlet 30 and further prevent the cold fluid from the external source 38 to flow directly in the main shell 18.

The secondary heat exchanger 22 is located at an end 16 of the main heat exchanger 12 and its purpose is to preheat the cold fluid (i.e., cold water or thermal oil) and to provide the preheated fluid 42 (i.e., preheated cold fluid to be provided to the main shell 18 from the plurality of secondary tubes 26) to the main heat exchanger 12. It is however to be noted that the secondary heat exchanger 22 may be located at the other end of the boiler 10, or at both ends of the boiler 10.

The secondary heat exchanger 22 includes a secondary shell 24 which is connected to the main shell 18 for receiving the cold fluid to be preheated. The secondary heat exchanger 22 further includes a plurality of secondary tubes 26 within the secondary shell 24 and is connected to the main heat exchanger 12. The plurality of secondary tubes 26 is for conveying the cold fluid and the secondary shell 24 is for conveying the recuperated gases 44 (i.e., the gases which lost energy by heating the preheated cold fluid within the main shell 18) which are recuperated from the plurality of primary tubes 20 of the main heat exchanger 12.

When the boiler 10 is in use, the hot gases 40 circulate in the furnace near the center of the main heat exchanger 12 then in the plurality of primary tubes 20 thereby heating the preheated fluid 42 (i.e., cold fluid which was preheated within the plurality of secondary tubes 26 of the secondary heat exchanger 22 and that is now in circulation within the main heat exchanger 12) and provides the recuperated gases 44 which circulates in the secondary shell 24 of secondary heat exchanger 22 for preheating the cold fluid. This configuration of the boiler 10 provides the preheated fluid 42 to circulate within the main shell 18 of the main heat exchanger 12 to be heated.

The main heat exchanger 12 includes two portions: a portion which is in cold fluid (shown in FIG. 6) and a portion which is in steam/vapor (shown in FIG. 6). According to an embodiment, the secondary heat exchanger 22 (i.e., the economizer) may be connected to the main heat exchanger 12 via a connection in the portion in cold fluid of the main heat exchanger 12 (i.e., lower header 48 of FIG. 4) and via a connection in the portion which is in steam of the main heat exchanger 12 upper header 50 of FIG. 4). The vapor exits the boiler 10 through boiler outlet 19 and is used by an external system.

According to another embodiment, fluid outlet of the secondary heat exchanger 22 is fluidly coupled to the main heat exchanger 12 via the portion which is in steam only.

According to another embodiment, the lower header 48 of the secondary heat exchanger 22 is fluidly connected to the main heat exchanger 12 via a flow restrictive device at the bottom of the main heat exchanger 12.

According to an embodiment, when the lower header 48 of the secondary heat exchanger 22 is connected to the main heat exchanger 12 through a flow restrictive device (i.e., orifice or check valve) the cold fluid flows upwardly by natural circulation into and through the secondary heat exchanger 22.

According to another embodiment, the secondary heat exchanger 22 may be of another kind of heat exchanger other than those made of tubes: for example, a plate exchanger.

According to an embodiment, the boiler 10 operates in a natural mode (i.e., operated via the natural circulation of the boiler 10) or, in a different embodiment, in a forced circulation mode (i.e., operated via pump equipment).

According to another embodiment, the secondary heat exchanger 22 is totally integrated in the main heat exchanger 12 of the boiler 10. The secondary heat exchanger 22 may include one or more baffles (not shown) to optimize heat transfer within the boiler 10.

The boiler 10 is usually installed in a closed circuit (not shown) for heating a fluid and delivering it through a boiler outlet 19 as an external flow. The fluid circulates in a network comprising radiators, exchangers or turbines which decrease the temperature of the fluid, then the fluid flows back into the boiler 10 through an external cold fluid inlet 30 to be heated again. According to an embodiment, the fluid is warm water or steam; it could also be a high specific heat capacity fluid or other convenient fluid or heating medium.

Referring to FIGS. 5 and 6 and according to an embodiment, the boiler 10 comprises a housing 13 enclosing the main heat exchanger 12 and secondary heat exchanger 22. The external cold fluid inlet 30 is connected to the lower header 48 of the secondary heat exchanger 22 for receiving the fluid coming from the network which is referred to as the cold fluid. A burner 34 produces hot gases 40, usually from combustion, which circulate among the plurality of primary tubes 20 for heating the preheated fluid 42. The preheated fluid 42 being heated in the main shell 18 naturally migrates from the bottom of main shell 18 to a higher section. The lower header 48 and the upper header 50 are fluidly connected to the main shell 18 for creating a high rate internal flow of the preheated fluid 42 upwardly from the lower header 48 to the upper header 50 by means of natural circulation where the cold fluid receives heat from the recuperated gases 44 exiting the main shell 18 flowing in the secondary shell 24 and exiting at the stack outlet 32 (aka chimney).

At the rear, at the front or at both ends, the boiler 10 comprises a secondary heat exchanger 22 (i.e., an secondary heat exchanger 22), also referred to as an additional exchanger receiving from the top, the bottom or the sides, recuperated gases 44 previously cooled by the plurality of primary tubes 20. The secondary heat exchanger 22 heats the cold fluid which, due to a difference in temperature between an economizer cold fluid inlet 49 and an economizer cold fluid outlet 51, naturally flows from the lower header 48 and up to the upper header 50 or, in another embodiment, by the use of an external pump.

Referring to FIG. 4 and according to an embodiment, there is shown one possible tube arrangement 36 of the secondary heat exchanger 22 of the boiler 10. The tube arrangement 36 comprises a plurality of secondary tubes 26 for conveying the cold fluid. Each of the plurality of secondary tubes 26 fluidly connects the lower header 48 and the upper header 50. The plurality of secondary tubes 26 may be connected to the headers 48, 50 by welding directly or by means of ferrules. According to an embodiment, the plurality of secondary tubes 26 comprises right and left inwardly extending portions each extending toward secondary shell 24. According to an embodiment, the tube arrangement 36 may be configured to include one or a plurality of different shapes (i.e., coils and the like).

Each one of the plurality of secondary tubes 26 can be staggered to another forming passages for the recuperated gases 44 to circulate around.

Still referring to FIGS. 1-4, the secondary heat exchanger 22 is located between the lower header 48 and the upper header 50 and comprises an economizer cold fluid inlet 49, an economizer cold fluid outlet 51, a hot gas inlet 60 and a hot gas outlet 62. The economizer cold fluid inlet 49 is fluidly connected to the lower header 48. The economizer cold fluid outlet 51 is fluidly connected to the upper header 50. According to another embodiment, the hot gas inlet 60, the hot gas outlet 62, the economizer cold fluid inlet 49 and the economizer cold fluid outlet 51 can be reversed.

In use, the previously cooled gases (i.e., recuperated gases 44) circulate through the secondary heat exchanger 22 and exhausts by the stack outlet 32. The cold fluid from an external source 38 is pumped upward from the lower header 48 to the upper header 50 crossing the economizer/secondary heat exchanger 22 thereby preheating the cold fluid. The external source 38 is fluidly connected to the external cold fluid inlet 30 for receiving additional cold fluid in the boiler 10 and inserting the additional cold fluid directly in the secondary heat exchanger 22 for pre-heating it before circulating in the tube arrangement 36. The external source 38 can also receive the cold fluid flowing back from the network instead of the external cold fluid inlet 30.

The boiler 10 may include multiple gas passage designs. The boiler 10 may include dry back, semi-wet back or wet back configurations. The boiler 10 may be configured for steam or hot water applications. The boiler 10 may have gaseous fuels, light or heavy oils firing capability. The boiler 10 may include optional electrical elements for bi-energy applications. The boiler 10 includes access doors at the front and at the back allowing full access to all primary and/or secondary tubes 20, 26. The burner 34 is fully serviceable without removing it.

The secondary heat exchanger 22 improves efficiency, reduces emissions of greenhouse gases, and reduces annual fuel costs.

The secondary heat exchanger 22 further offers the best payback available on the market by lowering the capital and operating costs.

The secondary heat exchanger 22 is fully serviceable from the rear and is easily removable to gain access to tubes.

According to another embodiment, the secondary heat exchanger 22 (i.e., the economizer) is completely integrated within the boiler 10. This configuration provides a boiler 10 which reduced costs since the secondary heat exchanger 22 does not need any external casing for covering it. Additionally, since the secondary heat exchanger 22 is completely integrated in the boiler 10, there is no need for additional piping systems between the different components and no additional installation procedures are to be performed on site.

According to another embodiment, the secondary heat exchanger 22 is connected to the main heat exchanger 12 via lower header 48 and upper header 50. The lower header 48 and upper header 50 allow for a natural circulation within the secondary heat exchanger 22 according to the communicating vessels principle. This is an important advantage since the secondary heat exchanger 22 and the boiler 10 can operate without operation of the pumping system for low flow rates (i.e., on/off type of cold fluid supply systems). The on/off type of cold fluid supply system is less expensive compared to a modulation cold fluid supply system which is required when the economizer is external to the boiler 10.

According to another embodiment, the secondary heat exchanger 22 may be made of a metallic or non-metallic material such as to include plastic, stainless steel, carbon steel and the like. The secondary heat exchanger 22 may include one or more baffles and/or one or more fins (not shown).

While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure. 

1. A boiler for heating a cold fluid with recuperated gases, the boiler comprising: a boiler gas exhaust providing an exhaust for the recuperated gases; and a secondary heat exchanger comprising: an economizer cold fluid inlet connected to a source of cold fluid; an economizer cold fluid outlet fluidly connected to the economizer cold fluid inlet and located thereabove, the cold fluid circulating upwardly from the economizer cold fluid inlet towards the economizer cold fluid outlet; a hot gas inlet for receiving the recuperated gases from the boiler gas exhaust; and a hot gas outlet fluidly connected to the hot gas inlet through the secondary heat exchanger, the recuperated gases circulating from the hot gas inlet toward the hot gas outlet; wherein the recuperated gases cross the secondary heat exchanger and exhaust by the hot gas outlet, the cold fluid being heated between the economizer cold fluid inlet and the economizer cold fluid outlet thereby resulting in a preheated fluid.
 2. The boiler of claim 1, wherein the secondary heat exchanger comprises a secondary shell for conveying the recuperated gases from the boiler gas exhaust.
 3. The boiler of claim 2, wherein the secondary heat exchanger comprises a plurality of secondary tubes between the economizer cold fluid inlet and the economizer cold fluid outlet and within the secondary shell, the plurality of secondary tubes being fluidly connected to the source of cold fluid.
 4. The boiler of claim 2, wherein main heat exchanger comprises a main shell receiving the preheated fluid.
 5. The boiler of claim 4, wherein the main shell comprises a boiler cold fluid outlet near a bottom portion of the main shell and the source of cold fluid is connected to the boiler cold fluid outlet and whereby the cold fluid flows upwardly by natural circulation into and through the secondary heat exchanger.
 6. The boiler of claim 5, further comprising an external cold fluid inlet wherein the source of cold fluid is also connected to external cold fluid inlet to admit cold fluid from an external source.
 7. The boiler of claim 6, further comprising a flow restrictive device located near the boiler cold fluid outlet and an external cold fluid inlet, the flow restrictive device letting the cold fluid flow from the boiler cold fluid outlet to the economizer cold fluid inlet when there is no fluid flow from the external source and, when the level of cold fluid is too low in the boiler, the cold fluid flows from the external source and the flow restrictive device will close to let the cold fluid flow from the external source through the external cold fluid inlet and further prevent the cold fluid from the external source to flow directly in the main shell.
 8. The boiler of claim 4, wherein the secondary shell is connected to or extends from the main shell.
 9. The boiler of claim 4, wherein the main shell and secondary shell form a single shell.
 10. The boiler of claim 4, wherein the main heat exchanger comprises two ends and the secondary heat exchanger is located at at least one of the two ends.
 11. The boiler of claim 1, further comprising a main heat exchanger for heating the preheated fluid, the main heat exchanger comprising the boiler gas exhaust and a burner for producing hot gases directed to the boiler gas exhaust.
 12. The boiler of claim 1, further comprising a lower header fluidly connected to the economizer cold fluid inlet.
 13. The boiler of claim 12, further comprising an upper header being fluidly connected to the economizer cold fluid outlet. 